Though Apple never mentioned the battery capacity on their website, during our review of the device we found that iPhone 8 does have 1821 mAh Li-Ion battery.
You will get about 51-52GB as free memory in case of iPhone 8 64GB. However, this is very much dependent on the software version.
Yes, you can use the old AirPods with the new iPhone 8.
No. iPhone 8 does not have the FM radio.
No longer the gold standard, the iPhone 8 is still all the phone you need.